World's Simplest Electric Train! The
system is simple enough, you have a battery sandwiched between two
polarized magnets running through a conductive loop of copper wire. As
soon as the battery and the magnet assembly enter the copper tunnel,
they complete a circuit
and now you have current running throughout the coil as the battery and
magnets induce an electromagnetic field. The copper coil forms a
solenoid (length of the battery), the solenoid now has its own magnetic
field that interacts with the magnets in the end. The resultant force
pushes the top magnet and pulls the bottom magnet but since the solenoid
is in between the magnets, it goes along with them throughout the loop
repeating the process.

Fun fact: if you reverse the polarities of both
magnets, you would make the "train" travel in an opposite direction. You
could also accelerate the train by either having a higher voltage
battery and or stronger magnets on the ends.

More: China already have a train that uses magnetic energy to move it. And Guess it's also the safest! No derailments.

This is an update regarding the Dinka. The Dinka are a Nilotic ethnic group from South Sudan.
They live from the tenth century on both sides of the Nile River and
speak a language belonging to the Nilo-Saharan group. They are about
three million and are divided into about 21 groups, each with its own
legitimate leader.
Although farming has always been its main economic resource, there
has never missed an important agricultural and fishing activity that
allowed them to be self-sufficient in food. Their trade and light
industry are increasingly gaining importance.
Photographers Carol Beckwith and Angela Fisher have an experience of
over 30 years recording ceremonies, rituals and daily life of African
tribal peoples. His photographs reflect a long and deep relationship of respect for the customs and people of these tribes, especially those of the Dinka:

Traditionally Dinka not wear many clothes, so it is normal for a grown
man to go completely naked except for collars around the neck. Women
usually wear only a goatskin from the waist. Increasingly, young women
are likely to adapt the dress forms from neighboring towns, and men, the
long robes worn in the north. They care a lot, especially men, about
body ornamentation. They usually remove some teeth by a purely cosmetic
issue. Men who are pastoralists, use cow dung ash to ward off
mosquitoes. It is easy to see men, especially among young people, with
dyed red hair, for what they use cow urine, while women shave their head
and eyebrows, leaving only a tuft of hair above her head.

Hummingbirds are New World birds that constitute the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm (3–5 in) range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm bee hummingbird, weighing less than a U.S. penny.

They are known as hummingbirds because of the humming sound created by their beating wings which flap at high frequencies audible to humans. They hover in mid-air at rapid wing-flapping rates, typically around 50 times per second, allowing them also to fly at speeds exceeding 15 m/s (54 km/h; 34 mph), backwards.

Hummingbirds have the highest metabolism of any homeothermic animal. To conserve energy when food is scarce, and nightly when not foraging, they go into torpor, a state similar to hibernation, slowing metabolic rate to 1/15th of its normal rate. [Source: Wikipedia]